Question

An aqueous solution of $CoC{l}_2$ on addition of excess of concentrated HCl turns blue due to formations of :

• A. $\left[Co\right(H_{2}O{)}_{4}C{l}_2]$
• B. $\left[Co\right(H_{2}O{)}_{2}C{l}_4{]}^{2-}$
• C. $[CoC{l}_4{]}^{2-}$
• D. $\left[Co\right(H_{2}O{)}_{2}C{l}_2]$

Answer 1

The correct option is C $[CoC{l}_4{]}^{2-}$

An aqueous solution of $CoC{l}_2$ on addition of excess of concentrated $HCl$ turns blue due to formations of
$[CoC{l}_4{]}^{2-}$. In $[CoC{l}_4{]}^{2-}$, the central $Co\left(II\right)$ ion
has $\left[Ar\right]3d^7$ electronic configuration.
In the tetrahedral field, it has 3 unpaired electrons.
It results in a blue colour.